JP2589986B2 - Magnetic recording media - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium.

[Prior art] A substrate for a magnetic disk and sputtering, plating,
A structure composed of a magnetic film and a protective film formed by a process such as vapor deposition is called a magnetic recording medium (hereinafter, referred to as a medium).

The magnetic storage device includes the medium and a recording / reproducing magnetic head (hereinafter, referred to as a head) as main components. At the start of the operation, the head and the medium are set in contact with each other, and then the medium is rotated as required to provide a required rotation. A space corresponding to an air layer is created between the head and the media surface, and recording and reproducing operations are performed in this state. At the end of the operation, the rotation of the medium stops, and at this time, the head and the medium return to the contact state as in the start of the operation (such a start / stop method is called a contact / start / stop CSS).

As described above, the contact frictional force generated between the head and the medium when the apparatus is started and stopped causes the head and the medium to be worn and causes deterioration of magnetic characteristics.

Further, when the medium is left in a humid atmosphere and moisture is adsorbed on the surface of the medium, water enters between the head and the medium, causing an adhesion phenomenon. Therefore,
If started in this state, a large resistance will be applied to the head and the medium, which may cause damage to the head and destruction of the medium.
Crash).

Generally, glass has attracted attention as a magnetic disk substrate suitable for high density because of its excellent surface smoothness, hardness, large deformation resistance, and few surface defects (Japanese Patent Application Laid-Open No. 49-122707, JP-A-52-18002).

However, for the above-described CSS resistance and head stick property, glass has excellent mirror finish, so the media using a glass substrate has a higher head than the media using other substrates having poor smoothness. However, there is a problem in that the contact area between the media and the media increases, thereby increasing the frictional resistance and the adhesive force.

In order to eliminate such drawbacks, the use of a glass substrate having fine irregularities formed on the surface by a mechanical method or a chemical method or a method using a combination of these methods allows the frictional force generated between the head and the medium to be reduced. Methods for reducing the adhesive force have been proposed.

When a relatively inexpensive glass containing alkali such as soda lime silica glass is used as the glass substrate, alkali ions are eluted from the exposed portion of the glass such as a pinhole portion of the magnetic film or a peripheral portion of the magnetic film in a humid environment. It has been found that this triggers the corrosion or deterioration of the magnetic film.

On the other hand, a glass substrate has a lower breaking strength than a substrate made of a conventional aluminum alloy or the like. Therefore, it is desirable to use a glass substrate having high strength, for example, a glass substrate that has been subjected to a strengthening treatment, as a measure for preventing damage to the spindle during mounting or other handling.

[Problems to be Solved by the Invention] As described above, the glass substrate must (1) not deteriorate the magnetic film due to humid environment or aging;
(2) It is required to have sufficient strength for practical use, and (3) to be able to form uniform irregularities on the surface.

As described above, when a relatively inexpensive alkali-containing glass is used as the glass substrate, the presence / presence of alkali ions on the glass surface or the migration / precipitation of alkali ions from the inside of the glass to the surface due to a humid environment or long-term use is prevented. In order to avoid the magnetic film deterioration, it is only necessary to use a glass having an extremely low alkali content, for example, a non-alkali glass.However, in that case, there is a problem such as a decrease in solubility during glass production. Yes, it is difficult to obtain inexpensive glass.

On the other hand, as a tempering treatment of the glass to obtain a practically sufficient strength, there are air cooling strengthening, liquid cooling strengthening and ion exchange strengthening. A so-called low-temperature ion exchange treatment is preferable as the strengthening treatment with a low risk of impairing the flatness of the thin glass substrate for a disk. The low-temperature ion exchange treatment of Na-containing glass is a treatment in which Na ⁺ ions in glass are exchanged with K ⁺ ions having a larger ion radius at a temperature lower than the glass transition temperature.

Since the alkali contained in the glass is a component that is ion-exchanged as described above, non-alkali glass cannot be a target of ion exchange strengthening. In addition, even if the glass contains an alkali, if the alkali content is low, a sufficient thickness of a compressive stress layer or a sufficient compressive stress cannot be obtained on the glass surface by ion exchange, and a practically sufficient strength cannot be obtained. .
Therefore, the substrate glass must be a glass containing alkali before the low-temperature ion exchange treatment is performed.

In addition, the above-described irregularities on the surface of the glass substrate do not include extremely large irregularities, and are required to be minute and uniform, and reproducibility and stability are also required for irregularities processing. Further, it is required that pits and fine cracks on the glass surface after the formation of the irregularities are as small as possible.

[Means for Solving the Problems] The present invention has been made to solve the above problems, and has a chemical composition of substantially SiO ₂ 65 to 75, Al ₂
O ₃ 4-9, B ₂ O ₃ 5-10, Na ₂ O 5-9.5, K ₂ O 0-3, Ba
A magnetic recording medium provided with a magnetic film on a glass substrate made of glass of O 3 to 6 and ZnO 0.5 to 3 and having uniform and minute irregularities formed on a main surface. It is.

The reasons for limiting each chemical component of the glass substrate in the present invention are as follows.

SiO ₂ is a glass network former, 65%
If it is less than 75%, the chemical durability decreases, and if it exceeds 75%, it becomes difficult to dissolve it. Al ₂ O _{3 not} only improves the chemical durability of the glass, but also increases the rate of ion exchange in which the alkali metal on the glass surface is replaced with an alkali metal having a larger ionic radius, and thus a deep compressive stress layer. And has an effect of easily forming, and 4% or more is essential. On the other hand, if it exceeds 9%, dissolution becomes difficult, which is not preferable. B ₂ O ₃ is required to be 5% or more in order to lower the viscosity of the glass and to improve the solubility and moldability. It is not preferable because durability is reduced.
Na ₂ O acts as a flux at the time of glass melting and is a main component that is ion-exchanged when performing ion exchange. If it is less than 5%, the solubility of the glass is lowered, and at the same time, a sufficiently thick compressive stress layer cannot be obtained by ion exchange, which is not preferable. In addition, the tendency of magnetic film deterioration is increased due to the increase in the amount of Na ⁺ ions deposited on the glass substrate surface, which is not preferable. K ₂ O is not an essential component, but by adding it improves the solubility of the glass,
Further, the speed of ion exchange can be improved. However, it should be within 3%, since excessive addition increases batch cost and reduces chemical durability. BaO acts as a flux at the time of glass melting and improves the chemical durability, so it should be contained at least 3%. If it exceeds 6%, it tends to be devitrified, and furthermore, the ion exchange rate is lowered, so it is preferable. Absent. ZnO
Has the effect of improving chemical durability. If the amount is less than 0.5%, the effect is insufficient. On the other hand, if it exceeds 3%, the solubility and the ion exchange rate decrease, so that both are not preferred. Therefore, ZnO is more preferably in the range of 0.5 to 3%. CaO and MgO may be present as impurities mixed from ordinary raw materials and during the process, as long as they are each 0.5% or less.

The glass according to the present invention accounts for 97% or more of the above components, and the remaining less than 3% can contain Li ₂ O or a commonly used fining agent, colorant, and the like. Li ₂ O can improve the solubility of glass by being added to the glass having the composition of the present invention described above, but is expensive, so even if added, it is within 0.5%, that is, 0 to 0.5%. Is desirable. The glass having the above-mentioned chemical composition in the present invention can be produced by, for example, a float method.

The glass substrate in the present invention is a plate-like glass having the above-mentioned chemical composition (this is referred to as a glass base plate) in which uniform and minute irregularities are formed on the main surface.

It is desirable that the above-mentioned minute unevenness has a maximum surface roughness height (Rmax) of 700 ° or less at a reference length of 250 μm and 50 ° or more at a reference length of 50 μm. The surface roughness here conforms to JIS B 0601 [Surface roughness]. Use a stylus type surface roughness meter with a nominal radius of 2.5 μm for the stylus, needle load 25 mg, sufficiently slow scanning speed The one obtained by the measurement will be adopted.

When Rmax is less than 50 °, the static friction characteristics of media and CS
Problems arise in the S characteristics and the stable flying characteristics of the magnetic head. On the other hand, in order to satisfy the magnetic characteristics such as the S / N ratio and the defect required for the medium and the low flying height of the magnetic head, Rmax is preferably about 1000 ° or less, and more preferably 700 ° or less.

Examples of the method of forming the irregularities include a hydrofluoric acid aqueous solution, an alkali fluoride, a chemical solution containing fluorine such as an alkali silicon fluoride or a chemical etching method using a hydrogen fluoride gas, Si
A mechanical method such as polishing with free abrasive grains such as C and Al ₂ O ₃ and a surface plate, or polishing with a lapping tape, or a combination of a chemical method and a mechanical method is used.

The magnetic recording medium of the present invention comprises a magnetic film and a protective film formed on the main surface of the glass substrate by a process such as sputtering, plating, or vapor deposition. Further, the upper part of the protective film can be covered with a lubricant. If necessary, an underlayer such as Cr may be provided between the glass substrate and the magnetic film. As the magnetic film, Co alloy, Co-Ni alloy, Co-Cr alloy, Co-Pt
Alloy, Co-Pt-Ni alloy or the like, as the protective film C, TiC, etc. SiO _2, and as the lubricant perfluoropolyether, perfluoro carboxylic acids, alkyl esters of perfluorocarboxylic acids can be used.

[Examples] Example 1. Preparation of sheet glass Glass is prepared and mixed according to a conventional method so as to obtain glasses having six kinds of compositions No. 1 to No. 6 shown in Table 1, and a glass batch is adjusted. did. Next, the glass batch is put into a Pt-Rh 10% crucible having a capacity of about 500 ml, melted at 1500 ° C. for about 4 hours including stirring for about 1 hour for homogenization, poured out onto a carbon plate to form a plate, and gradually cooled. Thereafter, it was cut and polished according to a conventional method to obtain a sheet glass sample having a thickness of about 1.9 mm.

Samples cut from the above plate-shaped glass sample and the same thickness of soda lime silica glass (NO.7, Comparative Example)
After performing ion exchange strengthening treatment by immersing in a KNO ₃ molten salt bath for 12 hours, a small piece of the sample was cut out, and the depth of the compressive stress layer was measured by a polarizing microscope. The values are shown in Table 1. Table 1 also shows the measured values of the strain points of the samples No. 1 to No. 7.

Example 2. Moisture resistance test of a magnetic recording medium (1) The sheet glass samples No. 1 to No. 6 and the sheet glass No. 7 obtained in Example 1 were cut and polished to obtain an outer diameter of 130 ×. Inner diameter 40
X A glass disk having a thickness of 1.9 mm was prepared. After cleaning and drying the glass disks NO.1 to NO.7, the glass substrate NO.1 having an irregular surface formed on the main surface of the disk by chemically etching using an aqueous solution containing potassium fluoride and hydrofluoric acid. ~ No. 7 were made respectively (referred to as unreinforced products or unreinforced products NO. 1 to NO. 7).

The maximum height (Rmax) of the surface roughness of these glass substrates NO.1 to NO.7 was within 500 mm when measured at a reference length of 250 μm, and was within 100 mm when measured at a reference length of 50 μm. .
The surface roughness was measured using a stylus having a radius of 2.5 μm, with a needle load of 25 mg and a sufficiently low scanning speed.

In addition, each part of the unreinforced products NO.1 to NO.7 thus obtained
A low-temperature ion exchange treatment was performed in a KNO ₃ bath (460 ° C × 12 hours) to produce reinforced glass substrates NO.1 to NO.7 (referred to as reinforced or reinforced products NO.1 to NO.7) .

On the main surface of each of the unreinforced product and the reinforced product, an underlayer made of about 1500 mm thick Cr is formed by sputtering, and then a Co-30 atomic% Ni alloy magnetic layer about 600 mm thick is formed. A magnetic recording medium was obtained by forming a carbon protective layer with a thickness of about 300 mm on top of it, and then forming a solid lubricating layer by plasma polymerization on the carbon protective layer (unreinforced magnetic recording medium or reinforced magnetic recording medium. Call).

A moisture resistance test was carried out on these at 80 ° C. and 90% RH. After 100 hours, the No. 7 unreinforced magnetic recording medium showed Co-Ni over a range of 1 to 2 mm from the inner and outer peripheral edges of the disk. Discoloration was observed at the interface between the alloy layer and the carbon layer. Similarly, discoloration of the NO. 7 reinforced magnetic recording medium was observed over a range of 0.5 to 1.5 mm from the peripheral portion. On the other hand, no color change was recognized in both the unreinforced product and the reinforced product of the magnetic recording media No. 1 to No. 6.

Example 3 Moisture resistance test of magnetic recording medium (2) Glass disks NO.
After washing and drying NO.7, a plurality of glass substrates NO.1 to NO.7 were made by forming concentric concave and convex portions on the main surface of the disk using # 3000 SiC wrapping tape. (Unreinforced or unreinforced products NO.1 ~
NO.7).

The maximum height (Rmax) of the surface roughness of these glass substrates NO.1 to NO.7 was within 500 ° or less when measured at a reference length of 250 μm and within 100 ° or more when measured at a reference length of 50 μm. .
The surface roughness was measured using a stylus having a radius of 2.5 μm, a needle load of 25 mg, and a sufficiently low scanning speed.

Glass substrates NO.1 to NO.7 reinforced by the same ion exchange treatment as in Example 2 were produced from each of the thus obtained unreinforced products NO.1 to NO.7 (reinforced products or reinforced products). NO.1
~ NO.7).

Forming an underlayer, a Co-Ni alloy magnetic layer, and a carbon protective layer of Cr having substantially the same thickness on the main surfaces of the unreinforced product and the reinforced product, respectively, in the same manner as in Example 2;
A liquid lubricating layer made of perfluoropolyether was provided thereon to obtain a magnetic recording medium (referred to as an unreinforced magnetic recording medium or a reinforced magnetic recording medium, respectively).

The magnetic recording medium thus obtained was subjected to a moisture resistance test under the same conditions as in Example 2. In the case of NO.7, both the unreinforced product and the reinforced product showed discoloration of the inner and outer peripheral edges of the disc and blue discoloration on almost the entire surface along with the texture in the main surface. On the other hand, in the case of the magnetic recording media No. 1 to No. 6, no discoloration was recognized at all on the inner and outer circumferences and in the plane of the unreinforced product and the reinforced product.

Example 4 Strength Test of Glass Substrate The unstrengthened and strengthened glass substrate having the above-mentioned irregularities was supported on the entire outer periphery of the disk and subjected to a bending strength test in which a load was applied to the inner periphery. Flexural strength of NO.7, compared to unreinforced product is about 14.5 kg / mm ^2, about the depth
The reinforced product having a 20 μm compressive stress layer was about 45 kg / mm ² .

In contrast, whereas unreinforced articles NO.1~NO.6 is about 14.5 kg / mm ^2, likewise reinforced article 460 ° C. × 12hrs. Treated product of about ^{35kg / mm 2, 480 ℃ ×} 12Hrs The processed product was about 36 kg / mm ² .

The stress based on the high-speed rotation of the disk-shaped magnetic recording medium (magnetic disk) is the maximum at the inner periphery and is the tensile stress in the direction of the dashed line. 5 1/4 inch size soda lime glass N
For O.7 disks, this tensile stress is 0.1 at 3600 rpm.
It is 25kg / mm ² about. Average tensile strength of scratched glass
Since this value is significantly lower than 7 kg / mm ² , it can be said that the glass is unlikely to be damaged by simple rotation.

If the glass substrate magnetic disk is damaged, it may be during the process until the magnetic disk is assembled into a drive device. Since glass does not actually undergo plastic deformation, it is more likely to be damaged than a A1 disc when concentrated stress is applied. Therefore, drive shafts, spacers, fasteners, etc., which may be subjected to strong forces to prevent such forces from acting. It is desirable that a material such as plastic is interposed in the contact portion with the material, or that a strong force is not applied. On the other hand, it is not preferable to handle the Al disk with plastic deformation due to the necessity of maintaining high precision dimensions.

From this point, a yield strength of Al of 10 kg / mm ² or more can be used as a guide as a strength required for the glass substrate magnetic disk.

According to the results of Example 4, the strength of the magnetic recording medium of the present invention is several times higher than the above 10 kg / mm ² , and it is recognized that the magnetic recording medium has the strength necessary for practical use.

Example 5. CSS test CSS characteristics, head stick property, S / N ratio, and missing pulse of the magnetic recording media of the present invention Nos. 1 to 6 and Comparative Example No. 7 obtained in the examples 2 and 3 Was evaluated. Table 2 shows the results.

[Effects of the Invention] 1) The magnetic recording medium of the present invention is extremely excellent in moisture resistance and aging resistance as compared with a magnetic recording medium using a general-purpose soda lime silica glass as a substrate.

2) The magnetic recording medium of the present invention has sufficient mechanical strength for practical use.

3) The surface unevenness of the glass substrate of the present invention can be formed with reproducibility and stability, and uniform unevenness can be provided on the main surface of the substrate.

4) The magnetic recording medium of the present invention is equal to or more than a magnetic recording medium using a general-purpose soda lime silica glass as a substrate in CSS characteristics, head stick properties, S / N ratio and defect evaluation.

5) The present invention provides an excellent magnetic recording medium in which moisture resistance, aging resistance, mechanical strength, and various characteristics required for a magnetic disk recording medium are practically balanced in a well-balanced manner.

Continuation of front page (56) References JP-A-61-77638 (JP, A) JP-A-62-65954 (JP, A) JP-A-61-63542 (JP, A) JP-A-62-43819 (JP) , A)

Claims (3)

(57) [Claims] 2. The method according to claim 1, wherein the chemical composition is substantially SiO ₂ 65 in weight%.
_{~75, Al 2 O 3 4~9,} B 2 O 3 5~10, Na 2 O 5~9.5,
K ₂ O 0~3, BaO 3~6, made of glass is a ZnO 0.5 to 3, characterized in that it magnetic film is provided on the uniform minute irregularities glass substrate formed on the main surface Magnetic recording medium. 2. The composition according to claim 1, wherein the chemical composition is substantially SiO ₂ 65% by weight.
_{~75, Al 2 O 3 4~9,} B 2 O 3 5~10, Na 2 O 5~9.5,
On a glass substrate obtained by subjecting a glass substrate made of glass of K ₂ O 0-3, BaO 3-6, and ZnO 0.5-3 to uniform and fine irregularities on the main surface to an ion exchange strengthening treatment, 2. The magnetic recording medium according to claim 1, wherein a magnetic film is provided. 3. The method according to claim 1, wherein the maximum height of the surface roughness comprising the uniform and minute unevenness is 700 ° or less at a reference length of 250 μm and 50 ° or more at a reference length of 50 μm. Item 3. The magnetic recording medium according to Item 1 or 2.